1. Field of the Invention
The present invention relates to a modulator and an electro-optic sensor equipped with a modulator, and more particularly to a modulator and an electro-optic sensor equipped with a modulator for detecting defects in liquid crystal display (LCD) panels and related semiconductor devices.
2. Discussion of the Related Art
An LCD panel contains numerous thin film transistors (TFTs) arranged in an array and pixel electrodes formed on a glass substrate. After the LCD panel is manufactured, a defect level in the LCD panel is diagnosed by an electro-optic sensor using a non-direct contact sensing method.
FIG. 1 is a broad view illustrating a conventional electro-optic sensor. As shown therein, the conventional electro-optic sensor 100 comprises a light source 14 for generating light, a modulator 10 for modulating the light from the light source 14 towards its mirror coating 10-3 and transmitting the light reflected from the mirror coating 10-3 at a certain ratio determined by the strength of its electric field, a beam splitter 12, a lens 16 for focusing the light emitted from the modulator 10, a CCD camera 17 for converting the focused light into an analog video signal, and an image processor 18 for converting the analog video signal into a digital video signal. The digital video signal is displayed on a monitor 20 for analysis.
FIG. 2 is a view illustrating a conventional modulator 10 of the electro-optic sensor 100. The modulator 10 includes a modulator body 10-2, a mirror coating 10-3 and a support frame 10-1. The modulator body 10-2 having a hexagonal shape is supported by the support frame 10-1. The mirror coating 10-3 formed of a thin metal foil is formed on the lower portion of the modulator body 10-2. The modulator body 10-2 includes an electrode commonly connecting with an external voltage source which supplies a reference voltage, and an electro-optic portion formed in the modulator body 10-2 for dispersing the incident light through the modulator body 102 and transmitting the reflected light towards the beam splitter 12 at a certain ratio determined by the strength of electric field in the modulator body 10-2.
The incident light from the light source 14 traverses the modulator body 10-2 and is reflected by the mirror coating 10-3. The reflected light traverses through the modulator body 10-2 and is emitted from the modulator 10 towards the beam splitter 12. During this process, the incident light traverses the modulator body 10-2 and is dispersed therethrough at a certain ratio determined by the strength of electric field in the modulator body 10-2. Consequently, the light emerging out of the modulator 10 has a level that is varied by the electric field strength of the modulator body 10-2.
An operation of the conventional electro-optic sensor and modulator will be explained below. The conventional electro-optic sensor 100 is positioned at a predetermined distance from the surface of the LCD panel 22. Then, a first voltage is applied to the LCD panel 22 as a detection voltage for detecting defects in the LCD panel 22, and a second voltage is also applied to the modulator 10 as a reference voltage. The detection and reference voltages establish a certain electric field in the area, and the electric field response is used to detect defects in the LCD panel 22 without directly emitting a detection signal at the LCD panel 22.
More specifically, when the detection voltage is applied to the picture elements of the LCD panel 22, the response of each picture element varies depending on the condition of the picture element, i.e., whether it is normal or has detects. As a result, each portion of the modulator 10 that corresponds to these picture elements has a different electric field strength. Under this condition, the light incident to the modulator 10 is output from the modulator 10 at a different level according to a predetermined ratio determined by the electric field strength of the modulator 10.
The light emitted from the modulator 10 is focused by the lens 16 and converted into an analog video signal by the CCD camera 17. The image processor 18 converts the analog video signal to a digital video signal. At this time, the condition of the LCD panel 22 is displayed on the monitor 20 based on the digital video signal and the image processing carried out by a central processing unit CPU (not shown). The monitor 20 helps to diagnose the degree of defectiveness in the LCD panel 22 because it displays normal and defective cells of the LCD panel 22 based on the light emerging from the modulator 10.
The conventional electro-optic sensor 20 carries out its operation using a non-contact sensing method since the electro-optic sensor 20 is positioned at a predetermined distance from the surface of the LCD panel 22. Generally, in conventional non-contact sensing methods, the distance between the mirror coating of the modulator and the surface of an LCD panel is no more than 20 .mu.m.
When a large foreign material (e.g., size equal to or bigger than 20 .mu.m) attaches to the surface of the LCD panel, the mirror coating of modulator is easily peeled off or damaged due to the contact with the foreign material. The damage to the mirror coating shortens the lifetime of the modulator of the electro-optic sensor. Further, the damaged mirror coating damages the LCD panel since an internal liquid of the modulator can flow out through the mirror coating and contaminate the LCD panel.